Surgical stapling instruments used for applying parallel rows of staples through compressed living tissue are well known in the art, and are commonly used, for example, for closure of tissue or organs prior to transection, prior to resection, or in anastomoses, and for occlusion of organs in thoracic and abdominal plasty procedures.
One known pneumo-intestinal surgical stapling instrument of this type has been in use for many years, and is currently available under the trade designation "The PI Stapler", catalog #3960 by Minnesota Mining and Manufacturing Company (3M), St. Paul, Minn., the use of which stapler is described in a publication entitled "Surgical Stapling, Gastric and Small Bowel Procedures, Volume I" ISBN 0-937433-00-4, Library of Congress Catalog Number 85-082599 available from Minnesota Mining and Manufacturing Company (3M), St. Paul, Minn., the contents of which are herein incorporated by reference. That stapler and a similar stapler described in Freund et al. PCT Application No. WO 83/02247, published July 7, 1983 are adapted for firing staples into compressed living tissue from a staple filled cartridge or housing.
"PI" type staplers have a handle lever, a generally C-shaped anvil portion having free and supported ends with an alignment aperture generally adjacent its free end, a cartridge transport member adapted to releasably receive a cartridge or staple housing having an alignment through passage, and an alignment pin movable between an engaged or alignment position with the alignment pin extending through the through passage in the staple housing and into the alignment aperture in the anvil jaw and a release or disengaged position with the alignment pin spaced from the alignment through passage and alignment aperture to afford removal and replacement of a spent staple cartridge.
The anvil and cartridge transport members are each elongate in a longitudinal direction, and the anvil portion has specially shaped anvil surfaces situated in a plane generally perpendicular to the longitudinal direction. When the alignment pin extends through the through passage in the staple housing and into the alignment aperture in the anvil jaw (i.e. when the alignment pin is in the alignment position), the specially shaped anvil surfaces are positioned generally opposite longitudinal slots in the cartridge or staple housing which contain unfired staples. The cartridge transport member/cartridge housing is movable between a closed or clamping position with the cartridge housing and the anvil surfaces in closely spaced relationship, and an open position with the cartridge housing and the anvil surfaces spaced farther from each other than in the closed position.
Typically, a "PI" type stapler is positioned adjacent the tissue to be stapled, the anvil and cartridge housing are approximated adjacent the tissue to be stapled, the alignment pin is moved to the alignment position, and the stapler is clamped on the tissue by moving the handle lever in a first movement to cause the cartridge holder to move toward the anvil placing the cartridge housing in the closed "clamping" position. Moving the handle lever in a second movement causes the stapler to be "fired" or causes the staples to be ejected from the cartridge.
In some surgical procedures the clamping force results in tissue that is highly compressed to ensure, inter alia, proper hemostasis in the tissues being stapled. Under a great clamping force, a prior art "PI" type stapler without an engaged alignment pin typically "scissors" or fails by deflection of the anvil portion and the cartridge housing laterally relative to one another (e.g. where the the anvil portion deflects laterally with respect to the longitudinal axis of the stapler and/or where the cartridge housing deflects in a lateral direction opposite the deflection direction of the anvil portion).
Moving the alignment pin to the alignment position before firing the stapler or before clamping tissue between the anvil and cartridge housing affords a more precisely controlled formation of the fired staples by aligning the specially shaped surfaces on the anvil portions with the staples in the cartridge housing and by preventing the cartridge housing and the specially shaped anvil surfaces from "scissoring". Moving the alignment pin to the alignment position also prevents tissue from escaping from between the anvil and cartridge housing when the cartridge assembly is clamped on the tissue to be stapled.
The prior art "PI" type staplers encounter problems because it is possible to fire the stapler or clamp tissue between the anvil and cartridge housing without the alignment pin in the alignment position. It is believed that it is difficult to determine whether the alignment pins of the prior art "PI" type staplers are engaged, particularly in the surgical environment. Also, it is possible to inadvertently fail to move the alignment pin to the alignment position. If the alignment pin is not moved to the alignment position before clamping tissue between the anvil and cartridge housing, tissue intended to be stapled may escape from between the anvil and cartridge housing resulting in incomplete anastomoses and other undesirable results. Additionally, if the alignment pin is not moved to the alignment position before the stapler is fired, the staples may be improperly formed.
Chow et al. U.S. Pat. No. 4,527,724 and assigned to Senmed, Inc., of Cincinnati, Ohio discloses a surgical stapler similar to the surgical stapler sold by Ethicon, Inc., of Somerville, N.J. under the trade name "Proximate". That stapler includes a lockout device which precludes rotation of an adjustment knob to clamp the stapler on tissue unless the alignment and retaining pin is shifted to its operative position. The lockout device, however, is only operative until the user slides the alignment and retaining pin to the operative position. Once the user slides the alignment and retaining pin to the operative position, the lockout device is not designed to be easily reactivated. Thus, to defeat the lockout device, a user need only slide the pin to the operative position and then away from the operative position. The stapler has no feature which retains the pin in the operative position when the stapler is clamped on tissue.